The move represents a new federal commitment to the low-carbon-emitting, but highly controversial, sector long championed by Republicans. Environmentalists voice concern.

Reporting from Los Angeles and Washington — Seeking common ground with Republicans on energy and climate issues, President Obama on Tuesday pledged $8 billion in loan guarantees needed to build the first U.S. nuclear reactors in nearly three decades.

The move, along with a tripling of nuclear loan guarantees in the president's budget, represents a new federal commitment to the low-carbon-emitting, but highly controversial, nuclear power sector long championed by the GOP.

Industry groups and Republican leaders praised the announcement, which has been expected for months, but some environmentalists and free-market think tanks protested.

Speaking at a training center at the Lanham, Md., headquarters of the International Brotherhood of Electrical Workers Local 26, the president spoke favorably of nuclear power as part of a mix of energy alternatives to oil.

"In order to truly harness our potential in clean energy, we'll have to do more," Obama said. "In the near term, as we transition to cleaner energy sources, we'll have to make tough decisions about opening new offshore areas for oil and gas development. We'll need to make continued investments in advanced biofuels and clean coal technologies, even as we build greater capacity in renewables like wind and solar.

"And we'll have to build a new generation of safe, clean nuclear power plants in America," he said.

Obama said his administration would supply about $8 billion in loan guarantees to build two new reactors at an existing nuclear power plant in Burke, Ga., providing thousands of construction jobs in the next few years and about 800 permanent jobs in the years to come.

Free-market groups complained that the loan guarantees could leave taxpayers on the hook for projects too risky for the private sector to finance.

Many environmentalists echoed the concerns and warned that the administration had not mapped a strategy for safe, long-term storage of radioactive waste.

"We're not really seeing anything but drawbacks to another corporate bailout that gives new meaning to the phrase 'toxic asset,' " said Jim Riccio, nuclear policy analyst for Greenpeace. "It is a dirty and dangerous distraction from the clean energy future the president promised America."

Obama noted environmentalist opposition in his remarks but insisted that clean, safe nuclear power was environmentally preferable to burning coal in outdated plants.

Many environmental groups were muted or subdued in their criticism Tuesday -- a reflection of the delicate politics surrounding ongoing efforts to pass energy and climate legislation in Congress.

Many large conservation groups appear to be tacitly accepting the need to increase federal nuclear support -- along with offshore oil and gas drilling, another environmentalist anathema -- to attract Republican votes for a measure to limit greenhouse gas emissions.